U.S. patent number 11,290,861 [Application Number 16/647,969] was granted by the patent office on 2022-03-29 for modulation and coding scheme (mcs) correction when sharing radio resources between mtc and non-mtc.
This patent grant is currently assigned to Nokia Sollutions and Networks Oy. The grantee listed for this patent is Nokia Solutions and Networks Oy. Invention is credited to Yigang Cai, Dongsheng Fan.
United States Patent |
11,290,861 |
Fan , et al. |
March 29, 2022 |
Modulation and coding scheme (MCS) correction when sharing radio
resources between MTC and non-MTC
Abstract
Systems, methods, and software for sharing resources of an air
interface. In one embodiment, an access network element
communicates with a plurality of devices over an air interface. The
access network element identifies a resource sharing window having
an MTC-On interval where MTC is allowed, and having an MTC-Off
interval where MTC is prohibited. Between a threshold time and an
end of the MTC-Off interval, the access network element selects an
adjusted Modulation and Coding Scheme (MCS) for a legacy device of
the plurality of devices that is lower than a standard MCS for the
legacy device selected based on channel quality information for the
legacy device, allocates a set of the MTC radio resources to the
legacy device, and schedules a non-MTC transmission for the legacy
device on the set of the MTC radio resources based on the adjusted
MCS.
Inventors: |
Fan; Dongsheng (Shanghai,
CN), Cai; Yigang (Naperville, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nokia Solutions and Networks Oy |
Espoo |
N/A |
FI |
|
|
Assignee: |
Nokia Sollutions and Networks
Oy (Espoo, FI)
|
Family
ID: |
65809587 |
Appl.
No.: |
16/647,969 |
Filed: |
September 19, 2017 |
PCT
Filed: |
September 19, 2017 |
PCT No.: |
PCT/CN2017/102234 |
371(c)(1),(2),(4) Date: |
March 17, 2020 |
PCT
Pub. No.: |
WO2019/056169 |
PCT
Pub. Date: |
March 28, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200221273 A1 |
Jul 9, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
1/0009 (20130101); H04L 1/0003 (20130101); H04W
72/12 (20130101); H04W 72/1263 (20130101); H04B
17/336 (20150115); H04W 4/70 (20180201); H04L
1/0015 (20130101); H04W 92/10 (20130101) |
Current International
Class: |
H04W
4/70 (20180101); H04B 17/336 (20150101); H04L
1/00 (20060101); H04W 72/12 (20090101); H04W
92/10 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102076028 |
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May 2011 |
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CN |
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106685587 |
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May 2017 |
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CN |
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WO 2011/097767 |
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Aug 2011 |
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WO |
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WO 2014/069946 |
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May 2014 |
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WO |
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WO 2018/203898 |
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Nov 2018 |
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WO |
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WO 2018/203899 |
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Nov 2018 |
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WO |
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Other References
International Search Report for PCT/CN2017/102234 dated Jun. 1,
2018. cited by applicant .
Huawei et al, Supporting FDM for MTC UEs and other UEs 3GPP Draft:
R1-150400, 3.sup.rd Generation Partnership Progject (3GPP), Mobile
Competence Centre; vol. RAN WG1 Feb. 8, 2015 XP050933609. cited by
applicant .
3rd Generation Partnership Project; Technical Specification Group
Radio Access Network; Evolved Universal Terrestrial Radio Access
(E-UTRA); Physical channels and modulation (Release 13)3GPP TS
36.211 V13.13.0 (Dec. 2019)--173 pp. cited by applicant .
3rd Generation Partnership Project; Technical Specification Group
Radio Access Network; Evolved Universal Terrestrial Radio Access
(E-UTRA); Multiplexing and channel coding (Release 13) 3GPP TS
36.212 V13.10.0 (Dec. 2019)--141 pp. cited by applicant .
ETSI TS 136213 V14.3.0 (Aug. 2017) Technical Specification LTE;
Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer
procedures 3GPP TS 36 213 V14.3.0 Release 14-462 pages
https://www.etsi.orq/deliver/etsi ts/13620 . . .
9/136213/14.03.00_60/ts_136213v140300p.pdf. cited by
applicant.
|
Primary Examiner: Ly; Anh Vu H
Attorney, Agent or Firm: Fay Sharpe LLP
Claims
What is claimed is:
1. An access network element of an access network, the access
network element comprising at least one processor; and, at least
one memory including computer program code; the at least one memory
and the computer program code configured to, with the at least one
processor, cause the access network element to: communicate with a
plurality of devices over an air interface; store a sharing pattern
that maps radio resources on a physical layer of the air interface
between Machine-Type Communications (MTC) radio resources and
non-MTC radio resources; identify a resource sharing window having
an MTC-On interval where MTC is allowed, and having an MTC-Off
interval where MTC is prohibited; and, between a threshold time and
an end of the MTC-Off interval, select an adjusted Modulation and
Coding Scheme (MCS) for a legacy device of the plurality of devices
that is lower than a standard MCS for the legacy device selected
based on channel quality information for the legacy device, to
allocate a set of the MTC radio resources to the legacy device
based on the sharing pattern, and to schedule a non-MTC
transmission for the legacy device on the set of the MTC radio
resources based on the adjusted MCS.
2. The access network element of claim 1 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to select
among multiple adjusted MCSs for the legacy device that are lower
than the standard MCS, and wherein the adjusted MCSs decrease from
the threshold time to the end of the MTC-Off interval.
3. The access network element of claim 2 wherein: a time period
from the threshold time to the end of the MTC-Off interval
comprises an adjustment period; the adjustment period comprises a
plurality of sub-periods in sequence that each specify a
signal-to-interference-plus-noise ratio (SINR) reduction value; and
SINR reduction values increase from a first one of the sub-periods
in the sequence to a last one of the sub-periods in the
sequence.
4. The access network element of claim 3 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to identify
the SINR reduction value for a sub-period of the plurality of
sub-periods, determine an estimated SINR for the legacy device
based on the channel quality information, subtract the SINR
reduction value for the sub-period from the estimated SINR to
determine an adjusted SINR for the legacy device, and select the
adjusted MCS for the legacy device based on the adjusted SINR.
5. The access network element of claim 4 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to determine
whether the SINR reduction value for the sub-period equals a
threshold value, and determine that the MTC radio resources are not
available to the legacy device when the SINR reduction value equals
the threshold value.
6. The access network element of claim 4 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to schedule
the non-MTC transmission for the legacy device on the set of the
MTC radio resources of an uplink channel.
7. The access network element of claim 4 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to schedule
the non-MTC transmission for the legacy device on the set of the
MTC radio resources of a downlink channel.
8. The access network element of claim 7 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to, between
the threshold time and the end of the MTC-Off interval: before
selecting the adjusted MCS for the legacy device, mark the MTC
radio resources as unavailable, allocate a set of the non-MTC radio
resources to the legacy device, select the standard MCS for the
legacy device, and determine a transport block size for the legacy
device based on the standard MCS; after selecting the adjusted MCS
for the legacy device, determine an adjusted transport block size
for the legacy device according to the adjusted MCS, and determine
whether the adjusted transport block size is increased over the
transport block size determined according to the standard MCS; and,
when the adjusted transport block size is not increased, allocate
the set of the MTC radio resources to the legacy device that were
previously marked as unavailable until the adjusted transport block
size is increased.
9. The access network element of claim 1 wherein the at least one
memory and the computer program code are configured to, with the at
least one processor, cause the access network element to request a
legacy load and an MTC load in the access network, determine
whether the legacy load exceeds a first high threshold, and set a
duration of the MTC-On interval for a next resource sharing window
to a minimum when the legacy load exceeds the first high threshold;
when the legacy load does not exceed the first high threshold,
determine whether the legacy load is less than a first low
threshold, and set the duration of the MTC-On interval for the next
resource sharing window to a maximum when the legacy load is less
than the first low threshold; when the legacy load is not less than
the first low threshold, determine whether the MTC load exceeds a
second high threshold, and increase the duration of the MTC-On
interval for the next resource sharing window when the MTC load
exceeds the second high threshold; when the MTC load does not
exceed the second high threshold, determine whether the MTC load is
less than a second low threshold, and decrease the duration of the
MTC-On interval for the next resource sharing window when the MTC
load is less than the second low threshold; and, when the MTC load
is not less than the second low threshold, maintain the duration of
the MTC-On interval in the next resource sharing window.
10. A method of sharing an air interface between an access network
element of an access network and a plurality of devices, the method
comprising: storing a sharing pattern that maps radio resources on
a physical layer of the air interface between Machine-Type
Communications (MTC) radio resources and non-MTC radio resources;
identifying a resource sharing window having an MTC-On interval
where MTC is allowed, and having an MTC-Off interval where MTC is
prohibited; between a threshold time and an end of the MTC-Off
interval, the method comprises: selecting an adjusted Modulation
and Coding Scheme (MCS) for a legacy device of the plurality of
devices that is lower than a standard MCS for the legacy device
selected based on channel quality information for the legacy
device; allocating a set of the MTC radio resources to the legacy
device based on the sharing pattern; and scheduling a non-MTC
transmission for the legacy device on the set of the MTC radio
resources based on the adjusted MCS.
11. The method of claim 10 wherein: selecting the adjusted MCS for
the legacy device comprises selecting among multiple adjusted MCSs
for the legacy device that are lower than the standard MCS; and the
adjusted MCSs decrease from the threshold time to the end of the
MTC-Off interval.
12. The method of claim 11 wherein: a time period from the
threshold time to the end of the MTC-Off interval comprises an
adjustment period; the adjustment period comprises a plurality of
sub-periods in sequence that each specify a
signal-to-interference-plus-noise ratio (SINR) reduction value; and
SINR reduction values increase from a first one of the sub-periods
in the sequence to a last one of the sub-periods in the
sequence.
13. The method of claim 12 wherein selecting the adjusted MCS
comprises: identifying the SINR reduction value for a sub-period of
the plurality of sub-periods; determining an estimated SINR for the
legacy device based on the channel quality information; subtracting
the SINR reduction value for the sub-period from the estimated SINR
to determine an adjusted SINR for the legacy device; and selecting
the adjusted MCS for the legacy device based on the adjusted
SINR.
14. The method of claim 13 further comprising: determining whether
the SINR reduction value for the sub-period equals a threshold
value; and determining that the MTC radio resources are not
available to the legacy device when the SINR reduction value equals
the threshold value.
15. The method of claim 13 wherein: scheduling the non-MTC
transmission for the legacy device comprises scheduling the non-MTC
transmission for the legacy device on the set of the MTC radio
resources of an uplink channel.
16. The method of claim 13 wherein: scheduling the non-MTC
transmission for the legacy device comprises scheduling the non-MTC
transmission for the legacy device on the set of the MTC radio
resources of a downlink channel.
17. The method of claim 16 wherein between the threshold time and
the end of the MTC-Off interval: before selecting the adjusted MCS
for the legacy device, the method comprises: marking the MTC radio
resources as unavailable; allocating a set of the non-MTC radio
resources to the legacy device; selecting the standard MCS for the
legacy device; and determining a transport block size for the
legacy device based on the standard MCS; after selecting the
adjusted MCS for the legacy device, the method comprises:
determining an adjusted transport block size for the legacy device
according to the adjusted MCS; determining whether the adjusted
transport block size is increased over the transport block size
determined according to the standard MCS; and when the adjusted
transport block size is not increased, allocating the set of the
MTC radio resources to the legacy device that were previously
marked as unavailable until the adjusted transport block size is
increased.
18. The method of claim 10 further comprising: requesting a legacy
load and an MTC load in the access network, determining whether the
legacy load exceeds a first high threshold, and setting a duration
of the MTC-On interval for a next resource sharing window to a
minimum when the legacy load exceeds the first high threshold; when
the legacy load does not exceed the first high threshold, the
method further comprises determining whether the legacy load is
less than a first low threshold, and setting the duration of the
MTC-On interval for the next resource sharing window to a maximum
when the legacy load is less than the first low threshold; when the
legacy load is not less than the first low threshold, the method
further comprises determining whether the MTC load exceeds a second
high threshold, and increasing the duration of the MTC-On interval
for the next resource sharing window when the MTC load exceeds the
second high threshold; when the MTC load does not exceed the second
high threshold, the method further comprises determining whether
the MTC load is less than a second low threshold, and decreasing
the duration of the MTC-On interval for the next resource sharing
window when the MTC load is less than the second low threshold;
when the MTC load is not less than the second low threshold, the
method further comprises maintaining the duration of the MTC-On
interval in the next resource sharing window.
19. A non-transitory computer readable medium embodying programmed
instructions executed by a processor, wherein the instructions
direct the processor to implement: an access network element of an
access network configured to communicate with a plurality of
devices over an air interface; the access network element is
configured to store a sharing pattern that maps radio resources on
a physical layer of the air interface between Machine-Type
Communications (MTC) radio resources and non-MTC radio resources;
and the access network element is configured to identify a resource
sharing window having an MTC-On interval where MTC is allowed, and
having an MTC-Off interval where MTC is prohibited; between a
threshold time and an end of the MTC-Off interval, the access
network element is operable to select an adjusted Modulation and
Coding Scheme (MCS) for a legacy device of the plurality of devices
that is lower than a standard MCS for the legacy device selected
based on channel quality information for the legacy device, to
allocate a set of the MTC radio resources to the legacy device
based on the sharing pattern, and to schedule a non-MTC
transmission for the legacy device on the set of the MTC radio
resources based on the adjusted MCS.
20. The non-transitory computer readable medium of claim 19
wherein: a time period from the threshold time to the end of the
MTC-Off interval comprises an adjustment period; the adjustment
period comprises a plurality of sub-periods in sequence that each
specify a signal-to-interference-plus-noise ratio (SINR) reduction
value; SINR reduction values increase from a first one of the
sub-periods in the sequence to a last one of the sub-periods in the
sequence; and the access network element is configured to identify
the SINR reduction value for a sub-period of the plurality of
sub-periods, to determine an estimated SINR for the legacy device
based on the channel quality information, to subtract the SINR
reduction value for the sub-period from the estimated SINR to
determine an adjusted SINR for the legacy device, and to select the
adjusted MCS for the legacy device based on the adjusted SINR.
21. The access network element of claim 1 comprising: at least one
of a base station, a wireless access point, and a base station and
associated controller.
22. A system comprising: a plurality of devices; and, an access
network element comprising at least one processor; and, at least
one memory including computer program code; the at least one memory
and the computer program code configured to, with the at least one
processor, cause the access network element to: communicate with
the plurality of devices over an air interface, store a sharing
pattern that maps radio resources on a physical layer of the air
interface between Machine-Type Communications (MTC) radio resources
and non-MTC radio resources, identify a resource sharing window
having an MTC-On interval where MTC is allowed, and having an
MTC-Off interval where MTC is prohibited, and, between a threshold
time and an end of the MTC-Off interval, select an adjusted
Modulation and Coding Scheme (MCS) for a legacy device of the
plurality of devices that is lower than a standard MCS for the
legacy device selected based on channel quality information for the
legacy device, allocate a set of the MTC radio resources to the
legacy device based on the sharing pattern, and schedule a non-MTC
transmission for the legacy device on the set of the MTC radio
resources based on the adjusted MCS.
Description
FIELD OF THE INVENTION
The invention is related to the field of communication systems and,
in particular, to sharing of radio resources between Machine Type
Communications (MTC) and non-MTC.
BACKGROUND
Machine Type Communications (MTC) or Machine-to-Machine (M2M)
communications refer to technologies that allow devices to
communicate with no or little human intervention. MTC devices store
data, and transmit the data to other MTC devices or an MTC server
over a network, such as a cellular network. For example, an MTC
device may be attached to a gas or electric meter, and the MTC
device periodically (e.g., weekly, monthly, etc.) transmits a meter
reading to an MTC server, such as at the utility company.
The amount of data exchanged between MTC devices is typically very
small, such as less than a few bytes. Because MTC devices send or
receive only small amounts of data, the exchanges of data are
considered "small data transmissions". The amount that is
considered "small" may depend on individual network operators.
MTC continues to increase over core networks. Thus, efficient use
of network resources for MTC, especially radio resources, is
important to network operators.
SUMMARY
Embodiments described herein provide enhanced sharing of radio
resources on the air interface between MTC transmissions and
non-MTC transmissions. A resource sharing window is defined for
scheduling radio resources between MTC and non-MTC. A resource
sharing window includes an MTC-On interval where MTC transmissions
are allowed, and an MTC-Off interval where MTC transmissions are
prohibited. Toward the end of an MTC-Off interval, the Modulation
and Coding Scheme (MCS) for a non-MTC device may be lowered to
increase the likelihood that a transmission involving the non-MTC
device is successfully received and decoded by the destination
(i.e., the device for a downlink transmission and a base station
for an uplink transmission). The MCS is typically selected for a
device based on channel quality identified for the device, and an
adjusted MCS as described herein is lower than the MCS which would
be selected based on channel quality. One technical benefit of
using an adjusted MCS toward the end of an MTC-Off interval is that
a Hybrid Automatic Repeat Request (HARQ) process for the
transmission will more likely complete before the end of the
MTC-Off interval, instead of being suspended during the next MTC-On
interval, to more efficiently utilize network resources.
One embodiment comprises an access network element of an access
network. The access network element includes a radio interface
component configured to communicate with a plurality of devices
over an air interface, and a pattern database configured to store a
sharing pattern that maps radio resources on a physical layer of
the air interface between MTC radio resources and non-MTC radio
resources. The access network element further includes a scheduling
mechanism configured to identify a resource sharing window having
an MTC-On interval where MTC is allowed, and having an MTC-Off
interval where MTC is prohibited. Between a threshold time and an
end of the MTC-Off interval, the scheduling mechanism is configured
to select an adjusted MCS for a legacy device of the plurality of
devices that is lower than a standard MCS for the legacy device
selected based on channel quality information for the legacy
device, to allocate a set of the MTC radio resources to the legacy
device based on the sharing pattern, and to schedule a non-MTC
transmission for the legacy device on the set of the MTC radio
resources based on the adjusted MCS.
In another embodiment, the scheduling mechanism is configured to
select among multiple adjusted MCSs for the legacy device that are
lower than the standard MCS, where the adjusted MCSs decrease from
the threshold time to the end of the MTC-Off interval.
In another embodiment, a time period from the threshold time to the
end of the MTC-Off interval comprises an adjustment period, the
adjustment period comprises a plurality of sub-periods in sequence
that each specify a signal-to-interference-plus-noise ratio (SINR)
reduction value, and SINR reduction values increase from a first
one of the sub-periods in the sequence to a last one of the
sub-periods in the sequence.
In another embodiment, the scheduling mechanism is configured to
identify the SINR reduction value for a sub-period of the plurality
of sub-periods, to determine an estimated SINR for the legacy
device based on the channel quality information, to subtract the
SINR reduction value for the sub-period from the estimated SINR to
determine an adjusted SINR for the legacy device, and to select the
adjusted MCS for the legacy device based on the adjusted SINR.
In another embodiment, the scheduling mechanism is configured to
determine whether the SINR reduction value for the sub-period
equals a threshold value, and to determine that the MTC radio
resources are not available to the legacy device when the SINR
reduction value equals the threshold value.
In another embodiment, the scheduling mechanism is configured to
schedule the non-MTC transmission for the legacy device on the set
of the MTC radio resources of an uplink channel.
In another embodiment, the scheduling mechanism is configured to
schedule the non-MTC transmission for the legacy device on the set
of the MTC radio resources of a downlink channel.
In another embodiment, before selecting the adjusted MCS for the
legacy device, the scheduling mechanism is configured to mark the
MTC radio resources as unavailable, to allocate a set of the
non-MTC radio resources to the legacy device, to select the
standard MCS for the legacy device, and to determine a transport
block size for the legacy device based on the standard MCS. After
selecting the adjusted MCS for the legacy device, the scheduling
mechanism is configured to determine an adjusted transport block
size for the legacy device according to the adjusted MCS, and to
determine whether the adjusted transport block size is increased
over the transport block size determined according to the standard
MCS. When the adjusted transport block size is not increased, the
scheduling mechanism is configured to allocate the set of the MTC
radio resources to the legacy device that were previously marked as
unavailable until the adjusted transport block size is
increased.
In another embodiment, the scheduling mechanism is configured to
request a legacy load and an MTC load in the access network, to
determine whether the legacy load exceeds a first high threshold,
and to set a duration of the MTC-On interval for a next resource
sharing window to a minimum when the legacy load exceeds the first
high threshold. When the legacy load does not exceed the first high
threshold, the scheduling mechanism is configured to determine
whether the legacy load is less than a first low threshold, and to
set the duration of the MTC-On interval for the next resource
sharing window to a maximum when the legacy load is less than the
first low threshold. When the legacy load is not less than the
first low threshold, the scheduling mechanism is configured to
determine whether the MTC load exceeds a second high threshold, and
to increase the duration of the MTC-On interval for the next
resource sharing window when the MTC load exceeds the second high
threshold. When the MTC load does not exceed the second high
threshold, the scheduling mechanism is configured to determine
whether the MTC load is less than a second low threshold, and to
decrease the duration of the MTC-On interval for the next resource
sharing window when the MTC load is less than the second low
threshold. When the MTC load is not less than the second low
threshold, the scheduling mechanism is configured to maintain the
duration of the MTC-On interval in the next resource sharing
window.
Another embodiment comprises a method of sharing an air interface
between an access network element of an access network and a
plurality of devices. The method comprises storing a sharing
pattern that maps radio resources on a physical layer of the air
interface between MTC radio resources and non-MTC radio resources,
and identifying a resource sharing window having an MTC-On interval
where MTC is allowed, and having an MTC-Off interval where MTC is
prohibited. Between a threshold time and an end of the MTC-Off
interval, the method comprises selecting an adjusted MCS for a
legacy device of the plurality of devices that is lower than a
standard MCS for the legacy device selected based on channel
quality information for the legacy device, allocating a set of the
MTC radio resources to the legacy device based on the sharing
pattern, and scheduling a non-MTC transmission for the legacy
device on the set of the MTC radio resources based on the adjusted
MCS.
In another embodiment, selecting the adjusted MCS for the legacy
device comprises selecting among multiple adjusted MCSs for the
legacy device that are lower than the standard MCS. The adjusted
MCSs decrease from the threshold time to the end of the MTC-Off
interval.
In another embodiment, a time period from the threshold time to the
end of the MTC-Off interval comprises an adjustment period, the
adjustment period comprises a plurality of sub-periods in sequence
that each specify a SINR reduction value, and SINR reduction values
increase from a first one of the sub-periods in the sequence to a
last one of the sub-periods in the sequence.
In another embodiment, selecting the adjusted MCS comprises
identifying the SINR reduction value for a sub-period of the
plurality of sub-periods, determining an estimated SINR for the
legacy device based on the channel quality information, subtracting
the SINR reduction value for the sub-period from the estimated SINR
to determine an adjusted SINR for the legacy device, and selecting
the adjusted MCS for the legacy device based on the adjusted
SINR.
In another embodiment, the method further comprises determining
whether the SINR reduction value for the sub-period equals a
threshold value, and determining that the MTC radio resources are
not available to the legacy device when the SINR reduction value
equals the threshold value.
In another embodiment, scheduling the non-MTC transmission for the
legacy device comprises scheduling the non-MTC transmission for the
legacy device on the set of the MTC radio resources of an uplink
channel.
In another embodiment, scheduling the non-MTC transmission for the
legacy device comprises scheduling the non-MTC transmission for the
legacy device on the set of the MTC radio resources of a downlink
channel.
In another embodiment, before selecting the adjusted MCS for the
legacy device, the method comprises marking the MTC radio resources
as unavailable, allocating a set of the non-MTC radio resources to
the legacy device, selecting the standard MCS for the legacy
device, and determining a transport block size for the legacy
device based on the standard MCS. After selecting the adjusted MCS
for the legacy device, the method comprises determining an adjusted
transport block size for the legacy device according to the
adjusted MCS, determining whether the adjusted transport block size
is increased over the transport block size determined according to
the standard MCS, and when the adjusted transport block size is not
increased, allocating the set of the MTC radio resources to the
legacy device that were previously marked as unavailable until the
adjusted transport block size is increased.
In another embodiment, the method further comprises requesting a
legacy load and an MTC load in the access network, determining
whether the legacy load exceeds a first high threshold, and setting
a duration of the MTC-On interval for a next resource sharing
window to a minimum when the legacy load exceeds the first high
threshold. When the legacy load does not exceed the first high
threshold, the method further comprises determining whether the
legacy load is less than a first low threshold, and setting the
duration of the MTC-On interval for the next resource sharing
window to a maximum when the legacy load is less than the first low
threshold. When the legacy load is not less than the first low
threshold, the method further comprises determining whether the MTC
load exceeds a second high threshold, and increasing the duration
of the MTC-On interval for the next resource sharing window when
the MTC load exceeds the second high threshold. When the MTC load
does not exceed the second high threshold, the method further
comprises determining whether the MTC load is less than a second
low threshold, and decreasing the duration of the MTC-On interval
for the next resource sharing window when the MTC load is less than
the second low threshold. When the MTC load is not less than the
second low threshold, the method further comprises maintaining the
duration of the MTC-On interval in the next resource sharing
window.
Another embodiment comprises a non-transitory computer readable
medium embodying programmed instructions executed by a processor,
wherein the instructions direct the processor to implement an
access network element of an access network configured to
communicate with a plurality of devices over an air interface. The
access network element is configured to store a sharing pattern
that maps radio resources on a physical layer of the air interface
between MTC radio resources and non-MTC radio resources. The access
network element is configured to identify a resource sharing window
having an MTC-On interval where MTC is allowed, and having an
MTC-Off interval where MTC is prohibited. Between a threshold time
and an end of the MTC-Off interval, the access network element is
configured to select an adjusted MCS for a legacy device of the
plurality of devices that is lower than a standard MCS for the
legacy device selected based on channel quality information for the
legacy device, to allocate a set of the MTC radio resources to the
legacy device based on the sharing pattern, and to schedule a
non-MTC transmission for the legacy device on the set of the MTC
radio resources based on the adjusted MCS.
Another embodiment comprises an access network element of an access
network. The access network element includes a means for
communicating with a plurality of devices over an air interface,
and a means for storing a sharing pattern that maps radio resources
on a physical layer of the air interface between MTC radio
resources and non-MTC radio resources. The access network element
includes a means for identifying a resource sharing window having
an MTC-On interval where MTC is allowed, and having an MTC-Off
interval where MTC is prohibited. Between a threshold time and an
end of the MTC-Off interval, the access network element includes a
means for selecting an adjusted MCS for a legacy device of the
plurality of devices that is lower than a standard MCS for the
legacy device selected based on channel quality information for the
legacy device, allocating a set of the MTC radio resources to the
legacy device based on the sharing pattern, and scheduling a
non-MTC transmission for the legacy device on the set of the MTC
radio resources based on the adjusted MCS.
The above summary provides a basic understanding of some aspects of
the specification. This summary is not an extensive overview of the
specification. It is intended to neither identify key or critical
elements of the specification nor delineate any scope of the
particular embodiments of the specification, or any scope of the
claims. Its sole purpose is to present some concepts of the
specification in a simplified form as a prelude to the more
detailed description that is presented later.
DESCRIPTION OF THE DRAWINGS
Some embodiments of the invention are now described, by way of
example only, and with reference to the accompanying drawings. The
same reference number represents the same element or the same type
of element on all drawings.
FIG. 1 illustrates a communication network in an illustrative
embodiment.
FIG. 2 illustrates radio resource sharing in an illustrative
embodiment.
FIG. 3 illustrates the LTE protocol stack.
FIG. 4 illustrates a DL LTE frame structure for the LTE air
interface.
FIG. 5 illustrates a Physical Resource Block (PRB) in a
time/frequency grid.
FIG. 6 illustrates a 5 MHz bandwidth in LTE.
FIG. 7 is a block diagram of an access network element in an
illustrative embodiment.
FIGS. 8-10 illustrate sharing patterns in an illustrative
embodiment.
FIG. 11 illustrates resource sharing windows divided into MTC-On
and MTC-Off intervals in an illustrative embodiment.
FIG. 12 is a graph illustrating how legacy usage affects resource
sharing windows in an illustrative embodiment.
FIG. 13 is a flow chart illustrating a method of updating a
resource sharing window in an illustrative embodiment.
FIG. 14 illustrates a resource sharing window with MCS correction
in an MTC-Off interval in an illustrative embodiment.
FIG. 15 is a flow chart illustrating a method of sharing radio
resources between MTC and non-MTC in an illustrative
embodiment.
FIG. 16 illustrates an adjustment period of an MTC-Off interval in
an illustrative embodiment.
FIG. 17 is a flow chart illustrating a method of selecting adjusted
MCSs during an adjustment period in an illustrative embodiment.
FIG. 18 is a flow chart illustrating a method of MCS correction for
UL transmissions in an illustrative embodiment.
FIG. 19 is a flow chart illustrating a method of MCS correction for
DL transmissions in an illustrative embodiment.
DESCRIPTION OF EMBODIMENTS
The figures and the following description illustrate specific
illustrative embodiments. It will thus be appreciated that those
skilled in the art will be able to devise various arrangements
that, although not explicitly described or shown herein, embody the
principles of the embodiments and are included within the scope of
the embodiments. Furthermore, any examples described herein are
intended to aid in understanding the principles of the embodiments,
and are to be construed as being without limitation to such
specifically recited examples and conditions. As a result, the
inventive concept(s) is not limited to the specific embodiments or
examples described below, but by the claims and their
equivalents.
FIG. 1 illustrates a communication network 100 in an illustrative
embodiment. Communication network 100 is a cellular network or
mobile network where the last link is wireless, and provides voice
and/or data services to a plurality of devices. Communication
network 100 is a Third Generation (3G), Fourth Generation (4G), or
later generation network, one example of which is a Long Term
Evolution (LTE) network.
Communication network 100 may provide an Internet of Things (IoT)
solution, which refers to interconnection and the autonomous
exchange of data between devices that are machines or parts of
machines. IoT uses Machine-to-Machine (M2M) communications or
Machine-Type Communications (MTC). M2M/MTC is defined as data
communication between devices without the human interaction.
Examples of M2M/MTC services include utility meters, vending
machines, fleet management, smart traffic, real-time traffic
information to a vehicle, security monitoring, medical metering and
alerting, etc. M2M/MTC services work well with lower data rates
than regular cellular services. For example, the Third Generation
Partnership Project (3GPP) has defined new categories for LTE in
Release 13, which include LTE Cat-M1 (eMTC) and Cat-NB1 (NB-IoT).
Cat-M1 (also referred to as LTE Cat 1.4 MHz) has a peak rate of 1
Mbps for uplink (UL) and downlink (DL), and a bandwidth of 1.4 MHz.
Cat-NB1 (also referred to as LTE Cat 200 kHz) has a peak rate of
200 kbps for DL, peak rate of 200 kbps for UL, and a bandwidth of
200 kHz. MTC-enabled devices may operate according to one of these
categories for MTC within communication network 100.
Communication network 100 also provides regular high-speed wireless
communications for devices and data terminals. For example, the LTE
standard set forth by the 3GPP defines Cat-4. Cat-4 (in Release 8)
has a peak rate of 150 Mbps for DL, a peak rate of 50 Mbps for UL,
and a bandwidth of 20 MHz. These "regular"
communications/transmissions in communication network 100 are
referred to herein as "legacy" transmissions. Legacy transmissions
are defined as non-MTC transmissions, such as voice calls,
streaming video, streaming audio, or other higher-speed
communications. Non-MTC devices may perform legacy transmissions
(e.g., Cat-4) for non-MTC within communication network 100.
Communication network 100 is illustrated as providing communication
services to devices 110-111 (along with other devices not shown)
located within the same cell. Device 110 is enabled for M2M/MTC
services, and is referred to as MTC device 110. MTC device 110 is
configured to send and receive various types of transmissions,
which may be referred to herein as MTC traffic or MTC
transmissions. For example, MTC transmissions may include small
data transmissions, such as sensor readings, temperature readings,
control signals, etc. Device 111 is enabled for regular voice
and/or data services, and is referred to as legacy device 111.
Legacy device 111 may include any wireless device not classified as
an MTC-enabled device. For example, legacy device 111 may include
end user devices such as laptop computers, tablets, smartphones,
etc. Legacy device 111 is configured to send and receive various
types of transmissions, which may be referred to herein as legacy
traffic, legacy transmissions, or non-MTC transmissions. For
example, legacy transmissions may include voice calls, audio,
video, multimedia, data, etc.
Communication network 100 includes one or more wireless access
networks 120 that communicate with devices 110-111 over radio
signals. One of the access networks 120 may be a Radio Access
Network (RAN) 122 that includes one or more base stations 123. Base
station 123 comprises an entity that uses radio communication
technology to communicate with a device on the licensed spectrum,
and interface the device with a core network. One example of RAN
122 is an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN)
having one or more Evolved-NodeBs (eNodeB), which are base stations
of the E-UTRAN.
Another one of the access networks 120 may be a Wireless Local Area
Network (WLAN) 126 that includes one or more Wireless Access Points
(WAP) 127. WLAN 126 is a network in which a device is able to
connect to a Local Area Network (LAN) through a wireless (radio)
connection. WAP 127 is a node that uses radio communication
technology to communicate with a device over the unlicensed
spectrum, and provides the device access to a core network. One
example of WAP 127 is a WiFi access point that operates on the 2.4
GHz or 5 GHz radio bands.
Devices 110-111 are able to attach to RAN 122 and/or WLAN 126 to
access a core network 130. In other words, access networks 120
represent the air interface between devices 110-111 and core
network 130. Core network 130 is the central part of communication
network 100 that provides various services to customers who are
connected by one (or more) of access networks 120. One example of
core network 130 is the Evolved Packet Core (EPC) network as
suggested by the 3GPP for LTE, although a core network for
later-generation networks are considered herein. Core network 130
includes one or more network elements 132, which comprise a server,
device, apparatus, or equipment (including hardware) that provides
services for devices 110-111. Network elements 132, particularly in
an EPC network, may comprise a Mobility Management Entity (MME), a
Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW), etc.
Within an EPC network, the user data (also referred to as the "user
plane") and the signaling (also referred to as the "control plane")
are separated. The MME handles the control plane within the EPC
network. For instance, the MME handles the signaling related to
mobility and security for E-UTRAN access. The MME is responsible
for tracking and paging mobile devices in idle-mode. The S-GW and
P-GW handle the user plane. The S-GW and P-GW transport IP data
traffic between devices 110-111 and external IP networks (not
shown). The S-GW is the point of interconnect between the
radio-side and the EPC network, and serves a device 110-111 by
routing incoming and outgoing IP packets. The S-GW is also the
anchor point for the intra-LTE mobility (i.e., in case of handover
between eNodeBs), and between LTE and other 3GPP accesses. The P-GW
is the point of interconnect between the EPC network and external
IP networks, and routes packets to and from the external IP
networks.
IoT services as provided by communication network 100 are projected
to be a driver for further growth in cellular, as billions of these
devices will be deployed in the future. Thus, many MTC devices will
be competing for radio resources of the air interface. For
LTE-based services, the basic premise is that MTC devices will use
specific radio resources of the air interface per 3GPP standards.
However, allocation of an entire radio channel for each MTC device
(or even a logical group of devices) can be expensive. Radio
channel demands for MTC services are very low and tend to be
sporadic due to the goal of conserving battery power on MTC
devices. Because the usage profile of MTC devices is sporadic and
involves small data transmissions, it may be beneficial to share
the UL and DL channels between MTC transmissions and regular,
legacy transmissions (e.g., LTE data traffic and VoLTE traffic).
Thus, an access network 120 can perform radio resource allocation
in a number of ways to share the radio resources of the air
interface between MTC transmissions and legacy transmissions (i.e.,
non-MTC transmissions).
FIG. 2 illustrates radio resource sharing in an illustrative
embodiment. FIG. 2 illustrates DL data transmissions from base
station 123 to MTC device 110 and legacy device 111. In this
embodiment, base station 123 provides a coverage area referred to
as a cell, and has established one or more radio channels 202 with
MTC device 110 and legacy device 111 that are located in the cell.
The radio channels 202 are physical connections of the air
interface 204 that are radio-based. Base station 123 also
determines a scheduling of radio resources on radio channels 202 so
that the radio resources are shared between MTC device 110 and
legacy device 111. Based on the scheduling, base station 123 may
send a transmission 210 over one or more of the radio channels 202
to MTC device 110 concurrently with sending a transmission 211 over
one or more of radio channels 202 to legacy device 111. The
transmissions 210-211 may share the radio resources of radio
channels 202, such as a frame in the time domain, and the system
bandwidth in the frequency domain, for an LTE air interface.
To understand radio resource sharing, FIGS. 3-6 illustrate the LTE
air interface as an example. FIG. 3 illustrates the LTE protocol
stack 300. For the user plane and the control plane, LTE protocol
stack 300 includes the Packet Data Convergence Protocol (PDCP)
layer 301, the Radio Link Control (RLC) layer 302, the Medium
Access Control (MAC) layer 303, and the physical layer 304. The
control plane will additionally include the Radio Resource Control
(RRC) layer (not shown in FIG. 3), which configures the lower
layers 301-304. Physical layer 304 offers data transport services
between an eNodeB and User Equipment (UE) to the higher layers
301-303. Data and signaling messages are carried on physical
channels between the different levels of physical layer 304. The
physical channels are divided into physical data channels and
physical control channels. The physical data channels include the
Physical Downlink Shared Channel (PDSCH), the Physical Broadcast
Channel (PBCH), the Physical Multicast Channel (PMCH), the Physical
Uplink Shared Channel (PUSCH), and the Physical Random Access
Channel (PRACH). The physical control channels include the Physical
Control Format Indicator Channel (PCFICH), the Physical Hybrid ARQ
Indicator Channel (PHICH), the Physical Downlink Control Channel
(PDCCH), and the Physical Uplink Control Channel (PUCCH). For MTC,
the physical control channels also include an MTC Physical Downlink
Control Channel (MPDCCH), which is a special type of PDCCH designed
for bandwidth-reduced operation.
LTE presently uses Orthogonal Frequency Division Multiplexing
(OFDM) for the DL physical channels to transmit data in parallel
over many closely-spaced sub-carriers using frames, and uses Single
Carrier Frequency Division Multiple Access (SC-FDMA) for UL
physical channels. FIG. 4 illustrates a DL LTE frame structure for
the LTE air interface. A frame 402 has an overall length of 10
milliseconds (ms). Frame 402 is divided into twenty individual
slots 404 (0.5 ms), and a sub-frame 406 is comprised of two slots
404. Thus, there are ten sub-frames 406 (1 ms) within each frame
402. Each Transmission Time Interval (TTI) consists of two slots
404 or one sub-frame 406 (1 ms). For a normal cyclic prefix, there
are seven OFDM symbols per slot 404. The OFDM symbols are grouped
into Physical Resource Blocks (PRB) 408 that are made up of
Resource Elements (RE) 410. REs 410 are the smallest modulation
structure in LTE. Each RE 410 is one subcarrier (e.g., 15 kHz) by
one OFDM symbol.
FIG. 5 illustrates a PRB 408 in a time/frequency grid 500. The time
domain is shown horizontally, and the frequency domain is shown
vertically in the grid 500 of FIG. 5. A PRB 408 includes twelve
sub-carriers (180 kHz in total) in the frequency domain, and one
slot 404 (0.5 ms) of 7 OFDM symbols in the time domain Thus, each
PRB 408 comprises eighty-four REs 410 (12.times.7). A PRB 408 is
the smallest unit of radio resources allocated to a UE. The more
PRBs 408 allocated to a UE, the higher bit-rate is available to the
UE. The number of PRBs 408 that are allocated to a UE at a given
point in time depends on scheduling mechanisms in the time and
frequency domains.
FIG. 6 illustrates a 5 MHz bandwidth in LTE. A 5 MHz bandwidth is
made up of three hundred subcarriers and twenty five PRBs 408. With
a total of twenty five PRBs 408, there are four narrowbands 602
(NB) available (the extra PRB is located at the center of the
system bandwidth). A narrowband 602 is defined as a set of six
contiguous PRBs 408. Thus, the LTE frame structure illustrated in
FIG. 4 is for one narrowband.
The PRBs 408 illustrated in FIGS. 4-5 may be used for the physical
data channels (e.g., PDSCH, PBCH, PUSCH, etc.) and the physical
control channels (e.g., PDCCH, PUCCH, MPDCCH, etc.) for the LTE air
interface. A scheduling mechanism will allocate the PRBs 408 for
the physical data channels and the physical control channels at any
point in time to send control information to UEs, to send data to
the UEs (DL), to receive data from the UEs (UL), etc.
For MTC, two major impacts are enormous amount of devices, and
limited data transmission per device. Within an LTE network,
introducing Cat-M1 into an LTE network may affect legacy traffic,
as Cat-M1 resource allocation competes with legacy LTE resources. A
network operator cannot tolerate degradation of legacy performance
when Cat-M1 traffic shares the same cell with legacy traffic.
Therefore, effective sharing of radio resources in a cell between
Cat-M1 traffic and legacy LTE traffic is a concern for network
operators. Embodiments described herein provide for an enhanced
scheduling mechanism for sharing radio resources between MTC (e.g.,
Cat-M1 transmissions) and non-MTC (i.e., legacy LTE transmissions)
over the air interface, such as an LTE air interface.
FIG. 7 is a block diagram of an access network element 700 in an
illustrative embodiment. Access network element 700 comprises any
node or collection of nodes of an access network (e.g., RAN 122 or
WLAN 126), such as a base station 123, a WAP 127, a base station
and associated controller, etc. Access network element 700 includes
a radio interface component 702, a controller 704 (including one or
more processors), a memory 706, and a network interface component
708. Radio interface component 702 represents the local radio
resources of access network element 700, such as transceivers and
antennas, used for wireless communications to exchange over-the-air
signals. Controller 704 represents the internal circuitry, logic,
hardware (e.g., a processor), software, etc., that provides the
functions of access network element 700. Memory 706 is a storage
unit for data, instructions, applications, etc., and is accessible
by controller 704 or other devices. Network interface component 708
is an interface component that provides an interface or backhaul
connection with a core network. The components of access network
element 700 may be implemented on the same hardware platform
(including one or more processors), or on separate platforms.
Controller 704 implements a scheduling mechanism 710. Scheduling
mechanism 710 comprises a device or set of devices that schedules
MTC transmissions and/or non-MTC transmissions via the radio
resources of an air interface, such as an LTE air interface.
Scheduling mechanism 710 may schedule only non-MTC transmissions
during certain scheduling windows to devices located within a cell.
Other times, scheduling mechanism 710 may schedule MTC and non-MTC
transmissions, in which case the radio resources are shared between
the MTC transmissions and the non-MTC transmissions. Although not
shown in FIG. 7, scheduling mechanism 710 may comprise one or more
processors, one or more blade servers, one or more Virtual Machines
(VM) running on a hardware platform, or other hardware devices.
In one embodiment, scheduling mechanism 710 may include an MTC
scheduler 712 and a legacy scheduler 714. MTC scheduler 712 is
configured to schedule MTC transmissions (e.g., physical data
channels and physical control channels) on the air interface.
Legacy scheduler 714 is configured to schedule non-MTC or legacy
transmissions (e.g., physical data channels and physical control
channels) on the same air interface. MTC scheduler 712 and legacy
scheduler 714 may comprise separate physical devices that are
connected by an interface (e.g., a proprietary interface). Each of
the separate physical devices may comprise one or more processors,
one or more blade servers, one or more VMs running on a hardware
platform, etc. MTC scheduler 712 and legacy scheduler 714 may
alternatively comprise a shared physical device that performs the
functions of both the MTC scheduler 712 and legacy scheduler
714.
Controller 704 may also include a pattern manager 720 and a pattern
database (DB) 722. Pattern manager 720 is configured to manage one
or more sharing patterns. A sharing pattern comprises a mapping of
radio resources between MTC and non-MTC on the physical layer of an
air interface. One assumption is that a multiple access modulation
format (e.g., OFDM, Non-Orthogonal Multiple Access (NOMA), etc.) is
used on the physical layer of the air interface that segments the
physical layer into radio resources in the time domain and in the
frequency domain. The radio resources may comprise PRBs, which have
both a time and a frequency dimension. The radio resources may
comprise sub-frames in the time domain, and narrowbands or
subcarriers in the frequency domain. A sharing pattern therefore
maps some radio resources to MTC and other radio resources to
non-MTC. For example, a sharing pattern may map or allocate a first
set of sub-frames to MTC only, and a second set of sub-frames to
non-MTC only on one or more narrowbands. The sharing patterns may
be predefined by pattern manager 720, by a network operator, etc.,
based on factors to maximize the use of the radio resources without
unacceptably impacting non-MTC transmissions on the air interface.
Pattern database 722 is configured to store one or more sharing
patterns (e.g., sharing patterns 1-4).
The sharing patterns map radio resources to MTC and non-MTC in the
time and frequency domains within a resource sharing window (e.g.,
a variable time period or number of TTIs). One or more sharing
patterns may fit in a resource sharing window depending on the
length of the resource sharing window. The sharing patterns may be
designed as bandwidth independent. The sharing patterns may
allocate radio resources for DL, UL, or both for control channels
and data channels. The sharing patterns may also include selection
criteria for selecting among a plurality of sharing patterns for a
resource sharing window. The selection criteria comprise any
characteristics, constraints, rules, etc., for selecting a sharing
pattern. The selection criteria may include operator-defined weight
factors, which allow the operator to increase or decrease MTC or
non-MTC for different resource sharing windows. The selection
criteria may include radio coverage conditions for MTC devices
within a cell (e.g., center, edge, CAT-M1 capability, etc.). The
selection criteria may include MTC traffic load and/or non-MTC
traffic load in an access network. The selection criteria may
include time-of-day (TOD), day-of-the-week (DOW), peak, off-peak,
etc. The selection criteria may include MTC or non-MTC
prioritization input from a network operator, DL/UL Hybrid
Automatic Repeat Request (HARQ) retransmission requirements,
Modulation and Coding Scheme (MCS) correction requirements, S1 and
paging transmissions, etc. The selection criteria may include cell
conditions, such as coverage, Signal-to-Interference-and-Noise
Ratio (SINR), whether a device is located in urban areas, remote
areas, etc. The selection criteria may include considerations for
mobility, eMBMS, VoLTE traffic, etc. The selection criteria may
include considerations for power saving requirements for
devices.
FIGS. 8-10 illustrate sharing patterns in an illustrative
embodiment. The mappings provided in FIGS. 8-10 are merely to
provide exemplary mappings, and resource sharing as described
herein is not limited to these sharing patterns. FIG. 8 illustrates
a sharing pattern 800 (or a portion of sharing pattern 800) in an
illustrative embodiment. In this embodiment, a mapping is provided
for the MTC control channel (MPDCCH), a DL data channel (PDSCH),
and a UL data channel (PUSCH). In a coverage enhancement mode, the
MPDCCH is repeated over a plurality of sub-frames to allow a UE to
determine the control information carried by the MPDCCH even in a
poor coverage area. The MDPCCH is an example of control
information, with the control information being any information
which schedules DL radio resources for radio transmission from a
base station to a UE and/or UL radio resources for radio
transmission from a UE to a base station. MPDCCH, PDSCH, and PUSCH
may be mapped to particular narrowbands/subcarriers which are not
specifically illustrated in FIG. 8. For this mapping, MPDCCH is on
a separate narrowband from PDSCH, MPDCCH repetition is four (with
R.sub.max=4), PDSCH repetition is four, PUSCH repetition is eight,
and the DL Invalid BL/CE sub-frame is at sub-frame seven. Sharing
pattern 800 has a 20 ms duration(=2 frames=20 sub-frames). The
example in FIG. 8 shows a resource sharing window of 40 ms so that
the repetition of pattern 800 is evident (i.e., pattern 800 is
repeated twice in the resource sharing window).
The mapping in the time domain for sharing pattern 800 is per
sub-frame. The sub-frames are illustrated as [0-9] for frame0 and
[0-9] for frame1. A "U" label in a sub-frame indicates a mapping of
that sub-frame for a UL MTC transmission, and a "D" label in a
sub-frame indicates a mapping for a DL MTC transmission. For
example, sub-frames [0-3] are mapped to the MPDCCH for UL MTC
control, and sub-frames [4-6, 8] are mapped to the MPDCCH for DL
MTC control. Sub-frames [7-14] are mapped to the PUSCH for UL MTC
data transmission, and sub-frames [10-16, 18] are mapped to the
PDSCH for DL MTC data transmission. The rest of the sub-frames that
are not specifically mapped to MTC control or data are available or
mapped to non-MTC (UL/DL) transmissions. Further, other radio
resources not shown in FIG. 8 may also be available or mapped to
non-MTC (UL/DL) transmissions.
FIG. 9 illustrates another sharing pattern 900 (or a portion of
sharing pattern 900) in an illustrative embodiment. In this
embodiment, the mapping is for UL MTC transmissions only. For
example, sub-frames [0-3] are mapped to the MPDCCH for UL MTC
control, and sub-frames [7-14] are mapped to the PUSCH for UL MTC
data transmission. The rest of the sub-frames that are not
specifically mapped to MTC control or data are available or mapped
to non-MTC (UL/DL) transmissions.
FIG. 10 illustrates another sharing pattern 1000 (or a portion of
sharing pattern 1000) in an illustrative embodiment. In this
embodiment, the mapping is for DL MTC transmission only. For
example, sub-frames [4-7] are mapped to the MPDCCH for DL MTC
control, and sub-frames [10-16, 18] are mapped to the PDSCH for DL
MTC data transmission. The rest of the sub-frames that are not
specifically mapped to MTC control or data are available or mapped
to non-MTC (UL/DL) transmission.
With the sharing patterns defined and stored in pattern database
722, scheduling mechanism 710 is able to schedule MTC transmissions
and non-MTC transmissions over the air interface to devices located
in the same cell of an access network (e.g., access network
120).
Scheduling mechanism 710 may use other policies to determine how
radio resources are shared between MTC and non-MTC on the air
interface. The resource sharing window may be dynamically divided
into variable lengths where MTC transmissions are allowed, and
where MTC transmissions are prohibited. Scheduling mechanism 710 or
pattern manager 720 may define an interval of the resource sharing
window where MTC is allowed. An interval is an amount of time in
the time domain (e.g., a number of TTIs, a number of sub-frames,
etc.). Scheduling mechanism 710 or pattern manager 720 may also
define an interval where MTC is prohibited. The intervals where MTC
transmissions are allowed are referred to as "MTC-On" or "Cat-M-On"
intervals, and MTC transmissions (control or data) are allowed to
be scheduled during these intervals. Legacy or non-MTC
transmissions may also be scheduled during the MTC-On intervals,
such as based on the sharing patterns described above. The
intervals where MTC transmissions are prohibited are referred to as
"MTC-Off" or "Cat-M-Off" intervals, and MTC transmissions (control
or data) are not allowed to be scheduled during these intervals.
MTC-On and MTC-Off intervals may be dynamically balanced based on
traffic at MTC scheduler 712 and/or legacy scheduler 714. An
algorithm is introduced herein to dynamically calculate the length
(e.g., number of TTIs) of the MTC-On and MTC-Off intervals for a
resource sharing window.
FIG. 11 illustrates resource sharing windows divided into MTC-On
and MTC-Off intervals in an illustrative embodiment. FIG. 11
illustrates two resource sharing windows 1101 that are configurable
in length. Within each resource sharing window 1101, there is a
configurable MTC-On interval 1110 and a configurable MTC-Off
interval 1112. An MTC-On interval 1110 and MTC-Off interval 1112
are sequential in time for the duration of a resource sharing
window 1101. Each interval 1110 and 1112 has a start time 1120
(i.e., a beginning) and an end time 1122 (i.e., an end). There is a
transition 1114 from an MTC-On interval 1110 to the next MTC-Off
interval 1112 within the same resource sharing window 1101, and a
transition 1116 from an MTC-Off interval 1112 to the next MTC-On
interval 1110 within the next resource sharing window 1101.
The resource sharing windows 1101 may fulfill the following
conditions: 1) Times of MPDCCH scheduling period (r.sub.max*G); and
2) Start from K0.
These conditions ensure that MTC transmissions may be scheduled
from the beginning of each resource sharing window 1101. In a
resource sharing window 1101, a portion of the time is for MTC
(i.e., MTC-On), and the other portion is for legacy or non-MTC
(MTC-Off). An MTC device may only be scheduled to use radio
resources that are mapped to MTC during MTC-On intervals 1110, such
as indicated in the sharing patterns above. A legacy device may use
radio resources that are mapped to MTC during MTC-Off intervals
1112. The duration of an MTC-On interval 1110 and an MTC-Off
interval 1112 may be updated for each resource sharing window
1101.
In defining the intervals for a resource sharing window 1101, the
minimum MTC-On interval 1110 may be defined as K*r.sub.max*G, where
K is an index controlled by a configurable parameter, r.sub.max is
maximum number of MPDCCH repetition given by a higher layer (e.g.,
RRC message), and G is the MPDCCH start sub-frame in common search
space given by the higher layer (e.g., RRC message). The minimum
length of an MTC-On interval 1110 should be long enough to
accommodate at least one UL or DL data transmission (it is not the
period that can guarantee to finish one HARQ process which can take
multiple retransmissions).
At the end of each resource sharing window 1101, scheduling
mechanism 710 may determine the duration of the MTC-On interval
1110 and MTC-Off interval 1112 in the next resource sharing window
1101. Scheduling mechanism 710 may determine legacy traffic load
and/or MTC traffic load when determining the duration of the MTC-On
interval 1110 and MTC-Off interval 1112 in the next resource
sharing window 1101. FIG. 12 is a graph 1200 illustrating how
legacy usage affects resource sharing windows in an illustrative
embodiment. Graph 1200 illustrates legacy usage or traffic load
over time. When legacy usage is low, scheduling mechanism 710 may
define an MTC-On interval for the entirety of the resource sharing
window 1101. As legacy usage increases, scheduling mechanism 710
may increase the MTC-Off interval and reduce the MTC-On interval
(i.e., based on an algorithm) in a resource sharing window 1101 to
ensure that MTC traffic does not unduly interfere with legacy
traffic. When legacy usage is high, scheduling mechanism 710 may
further reduce the MTC-On interval in a resource sharing window
1101.
FIG. 13 is a flow chart illustrating a method 1300 of updating a
resource sharing window in an illustrative embodiment. The steps of
method 1300 will be described with reference to access network
element 700 in FIG. 7, but those skilled in the art will appreciate
that method 1300 may be performed in other devices. Also, the steps
of the flow charts described herein are not all inclusive and may
include other steps not shown, and the steps may be performed in an
alternative order.
To begin, scheduling mechanism 710 requests the legacy load and/or
MTC load in a cell of an access network (step 1302). The legacy
load may be monitored by average PRB usage or average buffer size
waiting for grant in legacy scheduler 714. The MTC load may be
monitored by real-time usage during a prior MTC-On interval or
average buffer size waiting for grant in MTC scheduler 712.
Scheduling mechanism 710 determines whether the legacy load exceeds
a high threshold (step 1304). If the decision in step 1304 is
"yes", then scheduling mechanism 710 sets the duration of the
MTC-On interval for the next resource sharing window to a minimum
(step 1306). If the decision in step 1304 is "no", then scheduling
mechanism 710 determines whether the legacy load is less than a low
threshold (step 1308). If the decision in step 1308 is "yes", then
scheduling mechanism 710 sets the duration of the MTC-On interval
to a maximum (step 1310), which may be for the entirety of the next
resource sharing window. If the decision in step 1308 is "no", then
scheduling mechanism 710 determines whether the MTC load exceeds a
high threshold (step 1312). If the decision in step 1312 is "yes",
then scheduling mechanism 710 increases the duration of the MTC-On
interval for the next resource sharing window (step 1314), such as
by an increment or amount (e.g., number of TTIs). If the decision
in step 1312 is "no", then scheduling mechanism 710 determines
whether the MTC load is less than a low threshold (step 1316). If
the decision in step 1316 is "yes", then scheduling mechanism 710
decreases the duration of the MTC-On interval for the next resource
sharing window (step 1318), such as by an increment or amount
(e.g., number of TTIs). The increment size for increasing and
decreasing the duration of the MTC-On interval may be different and
is configurable, such as one MTC HARQ Round Trip Time (RTT). If the
decision in step 1316 is "no", then scheduling mechanism 710
maintains the durations of the MTC-On interval and the MTC-Off
interval in the next resource sharing window (step 1320). Method
1300 may then repeat for subsequent resource sharing windows to
accommodate charging traffic loads within a cell/access
network.
To summarize the above description, some radio resources (e.g.,
PRBs) of the air interface are mapped to MTC and other radio
resources are mapped to non-MTC or legacy transmissions, such as
indicated in the sharing patterns. Also, MTC-On and MTC-Off
intervals are defined for a resource sharing window. Scheduling
mechanism 710 considers the mapping of the radio resources between
MTC and non-MTC, and the MTC-On and MTC-Off intervals when
scheduling transmissions for devices in a cell. To schedule a
transmission for a device, scheduling mechanism 710 will consider
channel quality (i.e., radio conditions) and network load. Radio
conditions in a cell can impact bit rates available to a device
(better radio conditions allow for higher bit rates). A device may
report radio conditions to a base station (e.g., eNodeB) in the
form of a Channel Quality Indicator (CQI), such as for a DL
scheduling. The base station may also estimate channel quality for
uplink scheduling based on a Sounding Reference Signal (SRS), a
Demodulation Reference Signal (DMRS), etc. Scheduling mechanism 710
will select an MCS for the device based on channel quality. An MCS
that is selected for a device based on channel quality is referred
to herein as a "standard" MCS. An MCS is a combination of
modulation (e.g., QPSK, 64-QAM), coding rate (e.g., 1/2, 3/4),
guard interval (800 or 400 ns), number of spatial streams, etc. A
higher MCS means that more payload bits can be transmitted per time
unit. Scheduling mechanism 710 may use a lookup table to determine
a modulation and code rate based on the channel quality, such as
shown in Tables 7.2.3-2 and 7.2.3-3 in 3GPP TS 36.213 (version
14.3.0) for DL channels. Based on the modulation and code rate,
scheduling mechanism 710 may determine an MCS index for the
device.
Scheduling mechanism 710 also allocates a set of available radio
resources to the device, such as a number of PRBs (N.sub.PRB).
Scheduling mechanism 710 may determine a Transport Block Size (TBS)
for the device based on the MCS index and N.sub.PRB. TBS indicates
how many payload bits are transferred in a 1 ms (i.e., one TTI)
transport block size. To determine TBS, scheduling mechanism 710
may use a lookup table to determine a TBS index based on the MCS
index, such as shown in Tables 7.1.7.1-1 and 7.1.7.1-1A in 3GPP TS
36.213. Scheduling mechanism 710 may then use a lookup table to
determine a TBS based on the TBS index and N.sub.PRB, such as shown
in Table 7.1.7.2.1-1. At this point, scheduling mechanism 710 knows
how many bits can be transmitted per one TTI, and schedules UL and
DL transmissions for the device accordingly.
The MAC layer performs the modulation of data (i.e., the payload)
into the PRBs of the physical layer. The MAC layer (and higher
layers) also provides mechanisms to detect and correct errors in
the transmission of data. One mechanism is a HARQ process, which is
used to correct errors in data sent over the physical layer. For a
HARQ process, when a transmitting entity transmits data to a
destination using radio resources, the transmitting entity stops
and waits until it receives an acknowledgment (ACK) or negative
acknowledgement (NACK) back from the destination before
transmitting the next block of data or retransmitting the same data
block. If data is successfully received and decoded, then the
destination sends an ACK to the transmitting entity. If the data
has an error, then the destination buffers the data and requests a
re-transmission from the transmitting entity (NACK). When the
destination receives the re-transmitted data, it combines the
re-transmitted data with the buffered data prior to channel
decoding and error detection.
In the embodiments described herein, radio resources that are
mapped to MTC may be allocated to a legacy device during an MTC-Off
interval. If a HARQ process is not able to complete for a legacy
device during the MTC-Off interval, then the HARQ process will be
suspended to avoid collision with the next MTC-On interval where
these radio resources are to be used for MTC transmissions. The
suspension of HARQ processes will impact the performance of legacy
transmissions, and it is therefore desirable for the HARQ processes
for legacy devices to finish during an MTC-Off interval.
To assist the completion of HARQ processes for legacy devices
during an MTC-Off interval, MCS correction is implemented toward
the end of the MTC-Off interval. FIG. 14 illustrates a resource
sharing window 1401 with MCS correction in the MTC-Off interval in
an illustrative embodiment. As above, resource sharing window 1401
is comprised of a configurable MTC-On interval 1410 and a
configurable MTC-Off interval 1412. MTC-On interval 1410 and
MTC-Off interval 1412 each have a length in the time domain of one
or more TTIs 1414. Within each TTI 1414, some radio resources are
mapped to MTC (denoted by "M") and other radio resources are mapped
to non-MTC or legacy transmissions (denoted by "L"). MTC radio
resources and legacy radio resources may be scheduled to legacy
devices during MTC-Off interval 1412. MTC-Off interval 1412 has a
beginning 1420 and an end 1422, and a threshold time 1430 is
defined in MTC-Off interval 1412 before the end 1422 of MTC-Off
interval 1412, which is an amount of time, a number of TTIs, etc.
Between the threshold time 1430 and the end 1422 of MTC-Off
interval 1412, an adjustment period 1434 is defined. Adjustment
period 1434 is a time period toward the end 1422 of MTC-Off
interval 1412 where MCS correction may be performed. Adjustment
period 1434 is configurable, and may be adjusted by scheduling
mechanism 710, a network operator, etc.
FIG. 15 is a flow chart illustrating a method 1500 of sharing radio
resources between MTC and non-MTC in an illustrative embodiment.
The steps of method 1500 will be described with reference to access
network element 700 in FIG. 7, but those skilled in the art will
appreciate that method 1500 may be performed in other devices.
It is assumed in this embodiment that one or more sharing patterns
are defined as described above to map radio resources to MTC and
non-MTC. It is also assumed that one or more legacy devices have
attached to a cell of access network element 700. When scheduling
the radio resources for the devices that it serves, scheduling
mechanism 710 identifies a resource sharing window 1401 having an
MTC-On interval 1410 and/or an MTC-Off interval 1412 (step 1502).
Scheduling mechanism 710 may dynamically determine the resource
sharing window 1401 and the durations of MTC-On interval 1410 and
MTC-Off interval 1412 as described above, or may identify resource
sharing window 1401 as determined by another element (e.g., pattern
manager 720). During the resource sharing window 1401, scheduling
mechanism 710 will allocate radio resources to the TTIs of resource
sharing window 1401 sequentially from left to right in FIG. 14. The
time or TTI of resource sharing window 1401 at any point in time is
referred to as the scheduling time. As scheduling mechanism 710
proceeds through resource sharing window 1401, scheduling mechanism
710 determines whether the scheduling time is during an MTC-Off
interval 1412 (step 1504). If the scheduling time is not during an
MTC-Off interval 1412 and is during an MTC-On interval 1410, then
scheduling mechanism 710 schedules transmissions on radio resources
according to procedures for an MTC-On interval 1412 (step 1506),
which is outside the scope of this disclosure. If the scheduling
time is during an MTC-Off interval 1412, then scheduling mechanism
710 determines whether the scheduling time is during the adjustment
period 1434 (step 1508). If the scheduling time is before the
adjustment period 1434, then no MCS correction is performed (step
1510). With no MCS correction, scheduling may be performed as
follows. Scheduling mechanism 710 identifies a transmission request
for a legacy device (step 1512). The request may indicate the
payload to be sent to the legacy device for a DL transmission, or
the payload to be received from the legacy device for an UL
transmission. Scheduling mechanism 710 selects a standard MCS for
the legacy device based on channel quality information (e.g., CQI,
SRS, DMRS) for the legacy device (step 1514). The channel quality
information comprises any information indicating how good or bad
radio signals are for a communication channel. Channel quality
information may be reported by the legacy device, such as with a
CQI, or may be estimated based on signals exchanged with the legacy
device, such as with SRS and/or DMRS. Scheduling mechanism 710 also
allocates a set of radio resources (i.e., a number of radio
resources) to the legacy device (step 1516). During an MTC-Off
interval 1412, some or all of the radio resources allocated to the
legacy device may be mapped to MTC. For example, assume that four
PRBs are allocated to the legacy device. In this embodiment, one or
more of the PRBs allocated to the legacy device may be mapped to
MTC during an MTC-Off interval 1412. Scheduling mechanism 710 then
schedules a legacy transmission for the legacy device on the radio
resources based on the standard MCS (step 1518). This process may
repeat for multiple legacy devices during MTC-Off interval 1412
before adjustment period 1434.
If the scheduling time is during the adjustment period 1434, then
MCS correction is performed (step 1520). For MCS correction,
scheduling may be performed as follows. Scheduling mechanism 710
identifies a transmission request for a legacy device (step 1522).
Scheduling mechanism 710 selects an adjusted MCS (e.g., selects
among multiple adjusted MCSs) for the legacy device that is lower
than the standard MCS (step 1524). An adjusted MCS as described
herein is a lower or downgraded MCS as compared to the standard
MCS, which is selected based on channel quality. The adjusted MCS
may have a lower MCS index, may have a lower modulation, a lower
coding rate, etc. Scheduling mechanism 710 also allocates a set of
radio resources (i.e., a number of radio resources) to the legacy
device (step 1526). Again, some or all of the radio resources
allocated to the legacy device may be mapped to MTC. Scheduling
mechanism 710 then schedules a legacy transmission for the legacy
device on the radio resources based on the adjusted MCS (step
1528). This process may repeat for multiple legacy devices during
the adjustment period 1434.
By using a lower MCS during the adjustment period 1434 (i.e.,
toward the end of an MTC-Off interval 1412), radio resources (i.e.,
PRBs) for the legacy transmission will include less payload bits
and more redundancy and error correction bits. Thus, there is a
higher likelihood that the legacy transmission will be successfully
received and decoded at the destination (i.e., the legacy device or
base station). One technical benefit is that a HARQ process for the
legacy transmission will more likely complete before the end of the
MTC-Off interval 1412. Assume, for example, that a standard MCS is
selected for a legacy device based on channel quality (step 1514)
and the channel quality for the legacy device degrades (e.g., a
noisy environment). In this example, the destination may not be
able to successfully receive and decode the legacy transmission.
Thus, it will send a NACK during the HARQ process which will
trigger a re-transmission by the transmitting entity. The
destination will continue to send NACKs until the legacy
transmission is successfully received and decoded. But if channel
quality remains low, the HARQ process may not complete before the
end of an MTC-Off interval 1412, which is undesirable. To avoid
this situation, the MCS is lowered in the adjustment period, which
is toward the end of an MTC-Off interval 1412. With a lower MCS,
the radio resources include more redundancy/error correction bits
and less payload bits, which means it is more likely that a legacy
transmission will be successful received and decoded by the
destination. Thus, the HARQ process for the legacy transmission
will complete faster and before the end of an MTC-Off interval 1412
when an adjusted MCS is used.
During the adjustment period 1434, scheduling mechanism 710 may
select among a plurality of adjusted MCSs for the legacy device
that are lower than the standard MCS. The adjusted MCSs may
decrease (e.g., incrementally) from the threshold time 1430 to the
end of the MTC-Off interval 1412. One way to adjust MCS during the
adjustment period 1434 is to adjust SINR attributed to the legacy
device, as is further described in FIG. 16.
FIG. 16 illustrates the adjustment period 1434 of an MTC-Off
interval 1412 in an illustrative embodiment. In this embodiment,
adjustment period 1434 is a configurable time period from the
threshold time 1430 to the end 1422 of the MTC-Off interval 1412.
The length of adjustment period 1434 is shown as 50 TTI in this
example. Adjustment period 1434 comprises a plurality of
sub-periods 1601-1605 in sequence. The length of each sub-period
1601-1605 is configurable, and is shown as 10 TTIs in this example.
Each sub-period 1601-1605 specifies or defines a SINR reduction
value. For example, sub-period 1601 specifies a SINR reduction
value of 0.5 dB, sub-period 1602 specifies a SINR reduction value
of 1.0 dB, sub-period 1603 specifies a SINR reduction value of 1.5
dB, sub-period 1604 specifies a SINR reduction value of 3.0 dB, and
sub-period 1605 specifies a SINR reduction value of 5.0 dB. The
SINR reduction values increase from sub-period 1601 to sub-period
1605. Scheduling mechanism 710 may select an adjusted MCS during
the adjustment period 1434 using the SINR reduction values, as is
further described in FIG. 17.
FIG. 17 is a flow chart illustrating a method 1700 of selecting
adjusted MCSs during the adjustment period 1434 in an illustrative
embodiment. The steps of method 1700 will be described with
reference to access network element 700 in FIG. 7, but those
skilled in the art will appreciate that method 1700 may be
performed in other devices.
As described above, SINR is one metric used to determine the
channel quality for a device. When scheduling mechanism 710
receives a CQI for a device or estimates channel quality based on
SRS/DMRS, it can estimate an SINR for the device, and adjust the
SINR based on the SINR reduction value for a sub-period 1601-1605.
Thus, for a sub-period 1601-1605, scheduling mechanism 710
identifies the SINR reduction value for the sub-period (step 1701).
Scheduling mechanism 710 determines an estimated SINR for a device
based on channel quality information for the device (step 1702),
and subtracts the SINR reduction value for the sub-period from the
estimated SINR to determine an adjusted SINR for the device (step
1704). In one example, assume that the estimated SINR for the
device is 20 dB. For sub-period 1601, the SINR reduction value is
0.5 dB, so scheduling mechanism 710 would subtract 0.5 dB from 20
dB to determine an adjusted SINR of 19.5 dB. Scheduling mechanism
710 then selects an adjusted MCS for the device based on the
adjusted SINR (step 1706). For example, scheduling mechanism 710
may determine an adjusted CQI for the device based on the adjusted
SINR, and select the adjusted MCS based on the adjusted CQI, such
as with a lookup table shown in Tables 7.2.3-2 and 7.2.3-3 in 3GPP
TS 36.213. The adjusted MCS is lower than the standard MCS selected
for the device based on channel quality.
Scheduling mechanism 710 may repeat method 1700 during each
sub-period 1601-1605 of the adjustment period 1434. As the SINR
reduction values increase in the sub-periods 1601-1605, the
adjusted SINR for devices will decrease. In essence, the lower SINR
simulates a lower channel quality for the devices to scheduling
mechanism 710. Thus, the closer the scheduling time gets to the end
1422 of the MTC-Off interval 1412, a lower SINR is simulated for
the devices so that a lower MCS will be selected for the devices.
The lower MCS will help ensure that HARQ processes for the devices
will complete before the end of the MTC-Off interval 1412.
FIGS. 18-19 illustrate further details of how MCS correction may be
performed using the SINR reduction values shown in FIG. 16.
FIG. 18 is a flow chart illustrating a method 1800 of MCS
correction for UL transmissions in an illustrative embodiment. The
steps of method 1800 will be described with reference to access
network element 700 in FIG. 7, but those skilled in the art will
appreciate that method 1800 may be performed in other devices.
One assumption in this example is that scheduling mechanism 710 is
scheduling a transmission from a legacy device to access network
element 700 over a UL channel. Another assumption in this example
is that the scheduling time is during an adjustment period 1434 of
an MTC-Off interval 1412, such as shown in FIG. 16. For a
sub-period 1601-1605 of the adjustment period 1434, scheduling
mechanism 710 identifies the SINR reduction value for the
sub-period (step 1802). A predefined special value or threshold
value of y is defined (e.g., by a network operator) for an SINR
reduction value to indicate that legacy devices are not allowed to
use MTC radio resources, such as immediately preceding the end 1422
of an MTC-Off interval 1412. Scheduling mechanism 710 determines
whether the SINR reduction value for the sub-period equals the
special value of y (step 1804). If the SINR reduction value equals
the special value of y, then scheduling mechanism 710 marks the MTC
radio resources as unavailable for legacy transmissions/devices
(step 1806). If the SINR reduction value for the sub-period does
not equal the special value of y, then scheduling mechanism 710
allocates a set of radio resources (i.e., a number of radio
resources) to the legacy device (step 1808). Some or all of the
available radio resources allocated to the legacy device may be MTC
radio resources. Thus, scheduling mechanism 710 determines whether
MTC radio resources have been allocated to the legacy device (step
1810). If so, scheduling mechanism 710 subtracts the SINR reduction
value for the sub-period from the estimated SINR for the legacy
device to determine an adjusted SINR for the legacy device (step
1812). Scheduling mechanism 710 may then select an MCS (i.e., an
adjusted MCS) for the legacy device based on the adjusted SINR
(step 1814). If MTC radio resources have not been allocated to the
legacy device, then scheduling mechanism 710 selects an MCS (i.e.,
a standard MCS) for the legacy device based on channel quality
information (step 1814). When MTC radio resources are allocated to
the legacy device in step 1808, scheduling mechanism 710 will
schedule a UL legacy transmission by the legacy device using the
adjusted (i.e., lower) MCS. Thus, a HARQ process for this UL legacy
transmission is more likely to complete before the end of the
MTC-Off interval 1412.
FIG. 19 is a flow chart illustrating a method 1900 of MCS
correction for DL transmissions in an illustrative embodiment. The
steps of method 1900 will be described with reference to access
network element 700 in FIG. 7, but those skilled in the art will
appreciate that method 1900 may be performed in other devices.
One assumption in this example is that scheduling mechanism 710 is
scheduling transmissions from access network element 700 to legacy
devices over one or more DL channels. Another assumption in this
example is that the scheduling time is during an adjustment period
1434 of an MTC-Off interval 1412, such as shown in FIG. 16. For a
sub-period 1601-1605 of the adjustment period 1434, scheduling
mechanism 710 marks the MTC radio resources as unavailable for
legacy transmissions/devices (step 1902). Scheduling mechanism 710
allocates sets of legacy radio resources (i.e., a number of radio
resources or N.sub.PRB) to legacy devices (step 1904). Because the
MTC radio resources are indicated as unavailable, all of the
available radio resources allocated to the legacy devices at this
point are non-MTC or legacy radio resources. Scheduling mechanism
710 selects a standard MCS for each of the legacy devices based on
channel quality information (e.g., the CQI reported by the legacy
devices), and determines a TBS for each of the legacy devices based
on the standard MCS (step 1906). As described above, scheduling
mechanism 710 may determine a TBS for a device based on the MCS
index and N.sub.PRB. To determine TBS, scheduling mechanism 710 may
use a lookup table to determine a TBS index based on the MCS index,
such as shown in Tables 7.1.7.1-1 and 7.1.7.1-1A in 3GPP TS 36.213.
Scheduling mechanism 710 may then use a lookup table to determine a
TB S based on the TBS index and N.sub.PRB, such as shown in Table
7.1.7.2.1-1.
Scheduling mechanism 710 identifies the SINR reduction value for
the sub-period (step 1908). As before, a special value of y is
defined for an SINR reduction value to indicate that legacy devices
are not allowed to use MTC radio resources, such as immediately
preceding the end 1422 of an MTC-Off interval 1412. Scheduling
mechanism 710 determines whether the SINR reduction value for the
sub-period equals the special value of y (step 1910). If the SINR
reduction value equals the special value of y, then method 1900
ends. If the SINR reduction value for the sub-period does not equal
the special value of y, then scheduling mechanism 710 selects a
legacy device for MCS correction (step 1912). Scheduling mechanism
710 subtracts the SINR reduction value defined for the sub-period
from the estimated SINR for the legacy device to determine an
adjusted SINR for the legacy device (step 1914). Scheduling
mechanism 710 then selects an adjusted MCS for the legacy device
based on the adjusted SINR, and determines an adjusted TBS based on
the adjusted MCS (step 1916). Scheduling mechanism 710 determines
if the adjusted TBS has increased over the TBS previously
determined for the legacy device (step 1918). If TBS has increased,
then method 1900 ends. If TBS has not increased, then scheduling
mechanism 710 allocates a set of additional MTC radio resources,
which were previously marked as unavailable, to the legacy device
(step 1920). For example, if the legacy device was initially
allocated four legacy PRBs, scheduling mechanism 710 may allocate
an additional two MTC PRBs to the legacy device. Processing then
returns to step 1916 where scheduling mechanism 710 recalculates
TBS for the legacy device with the additional MTC radio resources.
This process of adding additional MTC radio resources and
re-calculating TBS continues until TBS has increased for the legacy
device.
Scheduling mechanism 710 ensures that TBS increases for a legacy
device even though MCS has been lowered with MCS correction (step
1918). If MCS is lowered, it is typically the case that TBS will
lower, which reduces throughput for the DL legacy transmission.
But, when additional MTC radio resources are allocated to the
legacy device (step 1920), TBS can be increased for the legacy
device even though MCS has been lowered so that throughput is not
reduced with the lower MCS. This advantageously allows scheduling
mechanism 710 to schedule the DL legacy transmission for the legacy
device using the adjusted (i.e., lower) MCS without reducing
throughput. Thus, a HARQ process for this DL legacy transmission is
more likely to complete before the end 1422 of the MTC-Off interval
1412.
Any of the various elements or modules shown in the figures or
described herein may be implemented as hardware, software,
firmware, or some combination of these. For example, an element may
be implemented as dedicated hardware. Dedicated hardware elements
may be referred to as "processors", "controllers", or some similar
terminology. When provided by a processor, the functions may be
provided by a single dedicated processor, by a single shared
processor, or by a plurality of individual processors, some of
which may be shared. Moreover, explicit use of the term "processor"
or "controller" should not be construed to refer exclusively to
hardware capable of executing software, and may implicitly include,
without limitation, digital signal processor (DSP) hardware, a
network processor, application specific integrated circuit (ASIC)
or other circuitry, field programmable gate array (FPGA), read only
memory (ROM) for storing software, random access memory (RAM),
non-volatile storage, logic, or some other physical hardware
component or module.
Also, an element may be implemented as instructions executable by a
processor or a computer to perform the functions of the element.
Some examples of instructions are software, program code, and
firmware. The instructions are operational when executed by the
processor to direct the processor to perform the functions of the
element. The instructions may be stored on storage devices that are
readable by the processor (i.e., a computer-readable medium). Some
examples of the storage devices are digital or solid-state
memories, magnetic storage media such as a magnetic disks and
magnetic tapes, hard drives, or optically readable digital data
storage media.
Although specific embodiments were described herein, the scope of
the disclosure is not limited to those specific embodiments. The
scope of the disclosure is defined by the following claims and any
equivalents thereof.
* * * * *
References